Improvement relating to projectile cartridge obturators and wads and cartridges employing such

ABSTRACT

An obturator for a projectile cartridge, such as a shotgun cartridge includes multiple seals that serve to prevent gas leakage past the obturator when the cartridge is fired, which in turn ensures more constant firing characteristics from one cartridge to the next. The obturator can be used in place of a powder card in a fibre wad based cartridge or it can be used a component part of a plastic wad in a plastic wad based cartridge, with both applications demonstrating improved gas sealing qualities. An associate method of manufacturing projectile cartridges with more constant ballistic characteristics is also provided.

PRIORITY

This application claims the priority of Great Britain patent application GB 2000379.4, filed Jan. 10, 2020, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to projectile cartridges, such as shotgun cartridges, and in particular obturators and wads used in the construction of the cartridges.

BACKGROUND OF THE INVENTION

As is known, shotgun cartridges typically comprise a projectile (e.g. a collection of lead or lead alloy shot), propellant powder (e.g. gunpowder) and a wad, all of which are housed within a tubular cartridge casing.

The role of the wad (also referred to as wadding) is to transfer the thrust generated by the gunpowder when it combusts to the shot so as to force the shot to exit the gun at speed. In order to ensure an efficient transfer of force, the wad is configured to form a seal, initially, with the cartridge case and, once the gun has been fired, the barrel of the gun.

When the seal formed by the wad is poor there can be gas leakage past the wad. This can lead to inconsistent ballistic results from one cartridge to the next, and other issues; such as increased recoil, lower performance and down-ranged striking energy.

There are two main types of wad employed in shotgun cartridges; the plastic wad and the fibre wad.

Plastic wads typically comprise a single moulded construction with three main parts, in the form of an obturator that is linked to a shot cup by way of a cushioning structure. With that said, in some moulded plastic wad constructions the cushioning structure may be omitted, particularly in situations where a larger shot cup is employed. It is the obturator that performs the sealing function when the gunpowder in the cartridge is ignited by the primer.

The moulded construction of plastic wads enables them to deliver a more consistent seal than fibre wads. Typically plastic wads have a standard deviation average of about 25 bar pressure between shots.

Fibre wads, on the other hand, typically have a two-part construction that comprises a powder card and a fibre driving wad. The powder card, which is typically just stamped out in a circular disc shape, acts as a barrier between the gunpowder and the fibre driving wad. The fibre wad provides a cushioning function to protect the shot from being deformed by the forces generated by the exploding gunpowder.

Unfortunately, the quality of the seal formed by the fibre wad, and in particular the powder card, is not as good as that achieved by a plastic wad. As a consequence, cartridges with fibre wads offer less consistent results than shotgun cartridges with plastic wads. Typically fibre wads offer with a standard deviation average of about 40 bar pressure between shots.

Despite their lower reliability, however, fibre wads are still commonly used. This is primarily due to the environmental issues relating to plastic wads, which do not degrade in the same way as fibre wads.

SUMMARY OF THE INVENTION

With a view to delivering more consistent performing projectile cartridges, the present invention provides an improved projectile cartridge obturator.

The projectile cartridge obturator according to certain embodiments includes: a main body having a first face, with a first centrally located projection spaced apart from a first annular skirt portion located on the periphery of the main body, and a second face, with a second centrally located projection spaced apart from a second annular skirt portion located on the periphery of the main body; wherein the free end of each annular skirt portion is configured to form a seal with the interior wall of a projectile cartridge case when the obturator is inserted into the case; and wherein the first annular skirt portion is further provided with a secondary seal spaced away from the free end of the first skirt portion, said secondary seal also configured to form a seal with the interior wall of the cartridge case.

The provision of multiple sealing means on the obturator delivers a reduction in gas leakage when the cartridge is fired, which helps to provide more consistent ballistic results from one cartridge to the next.

Providing a seal on the free end of each skirt allows the explosive gases generated by the gunpowder when it ignites to get behind the skirt and urge the seal outwards to improve the seal formed, initially, against the surrounding walls of the cartridge casing and, subsequently, the gun barrel. By providing at least one skirt with an additional secondary seal at a different location on the skirt, the explosive gases can be harnessed to urge both the skirt's main seal and the secondary seal outwards.

Preferably the second annular skirt portion may also be provided with a secondary seal spaced away from the free end of second annular skirt portion, wherein said secondary seal is also configured to form a seal with the interior wall of the case.

It is has been found that the obturator as disclosed herein helps to greatly reduce the gas leakage in shotgun cartridges in a consistent manner. Tests have shown that cartridges employing the obturator as disclosed herein have demonstrated an improved standard deviation average in the region of 5 bar pressure between shots.

Preferably the obturator further comprises a vent in one or more of the seals formed by the first and second annular skirt portions and the secondary seals. The vent may take the form of a groove or channel (located in the obturator) that traverses each seal.

The provision of a vent in one or more of the main or secondary seals is considered beneficial to the cartridge manufacture process, and in particular the manufacturing step of inserting the obturator into a cartridge case.

Due to the increased sealing achieved by the provision of multiple seals around the perimeter of the obturator, air can become trapped within the case when the obturator is inserted. This can lead to technical difficulties during the cartridge manufacture process which can introduce imperfections into the obturator or the cartridge case that impair the quality of the obturator's gas sealing properties.

It is envisioned that providing one or more vents in the seals of the obturator is sufficient to allow air to escape from the cartridge at the speeds associated with the insertion step but not at the greater speeds associated with the firing of the cartridge.

As a result, the provision of vents in the seals facilitates the cartridge manufacture process without reducing the gas sealing properties of the final cartridge product during use.

Preferably each of the seals of the obturator is provided with a vent to facilitate the escape of air during the obturator insertion step.

In situations where more than one of the seals is provided with a vent, it is considered particularly preferable that the vents on adjacent seals are offset from one another around the periphery of the obturator. By offsetting the vents in this way it is possible to create a more torturous path around the obturator.

Again, the torturous or ponderous path taken by gases trying to pass the obturator has less of an impact at the speeds associated with the insertion of the obturator into the cartridge case than it does at the faster speeds associated with the firing of the cartridge.

In this way the obturator provides improved sealing when needed (i.e. during the combustion of the gun powder) without impeding the manufacture of the cartridge.

Preferably the first and/or second centrally located projection may comprise cut out regions that define one or more structural ribs. In this way the amount of material required to form the obturator can be reduced without impairing the structural strength of the obturator. It is envisioned that alternative centrally located projections may be provided with alternative structure arrangements by making different cut out regions. For example, in one preferred alternative the cut outs may define one or more co-axially located circular projections.

Either way, reducing the amount of material used to form the obturator makes it more economically viable to construct the obturator from a biodegradable polymer material, which might otherwise be commercially unattractive due to manufacturing costs.

It is envisioned that it is particularly preferable to form the obturator from a biodegradable polymer material when it is used in place of the powder card in a fibre wad. With that said, the obturator, whether in a biodegradable form or not, can be used in both plastic wads and fibre wads.

The disclosure also includes a projectile cartridge wad that comprises the projectile cartridge obturator. In this aspect the cartridge wad may comprise either a fibre wad or a plastic wad.

In the case of a fibre wad for a projectile cartridge the wad further comprises a fibre plug.

In the case of plastic wad for a projectile cartridge the wad further comprises a shot cup.

Preferably the plastic wad may further comprise a cushioning structure that is located between the obturator and the shot cup. Further preferably the cushioning structure is connected to the second centrally located projection of the obturator.

Further preferably the obturator, cushioning structure, when present, and the shot cup are formed as a single moulded piece.

For situations where a cushioning structure is not required a projectile cartridge obturator is provided comprising: a main body having a first face, with a first centrally located projection spaced apart from a first annular skirt portion located on the periphery of the main body, and a second face, upon which a shot cup is provided, with a second annular skirt portion located on the periphery of the main body; wherein the free end of each annular skirt portion is configured to form a seal with the interior wall of a projectile cartridge case when the obturator is inserted into the case; and wherein the first annular skirt portion is further provided with a secondary seal spaced away from the free end of the first skirt portion, said secondary seal also configured to form a seal with the interior wall of the cartridge case. In the above arrangement it will be appreciated that the second face of the obturator defines the base of the shot cup, thereby allowing the length of the shot cup to be maximised within the size restrictions of the complete projectile cartridge.

A projectile cartridge can include the obturator or wad as disclosed herein.

The disclosure further includes a method of manufacturing a projectile cartridge. The method can include: moulding an obturator from a polymer material, said obturator comprising a main body having a first face, with a first centrally located projection spaced apart from a first annular skirt portion located on the periphery of the main body, and a second face, with a second centrally located projection spaced apart from a second annular skirt portion located on the periphery of the main body, and wherein at least the first annular skirt portion is provided with a secondary seal spaced away from the free end of the first annular skirt; inserting the obturator into a projectile cartridge case between a charge of gunpowder and one or more cartridge projectiles (e.g. shot) such that the free ends of the annular skirts and said at least one secondary seal form seals with the interior wall of the cartridge case; and closing the case to encapsulate its contents.

Preferably the second annular skirt portion may also be provided with a secondary seal spaced away from the free end of second skirt portion, wherein said secondary seal is also configured to form a seal with the interior wall of the case.

Preferably the method may further comprise providing each of the annular skirts and said at least one secondary seal with a vent. As noted above, the provision of one or more vents in the obturator's seals makes the step of inserting the obturator into the cartridge case, with which it forms a sealing relationship, easier.

Further preferably, the vents provided in adjacent seals may be offset from one another around the periphery of the obturator. As noted above, arranging the vents in this way helps to define a torturous gas flow path around the obturator, which reduces gas leakage.

Additionally or alternatively, it is considered preferable that the first centrally located projection, and further preferably the second centrally located projection too, may be moulded with cut outs that define one or more structural ribs. It is envisioned that alternative structural arrangements may be provided by adopting different cut outs.

As noted above, reducing the amount of material required to manufacture the obturator can significantly reduce cartridge manufacturing costs, particularly in situations where the obturator is moulded from a biodegradable polymer material.

Preferably a fibre plug may be provided between the obturator and the cartridge projectile. Alternatively, the obturator may be moulded as part of a combined wad component that also comprises a shot cup, in which said one or more cartridge projectiles are received. Preferably, the combined wad component may also comprise a cushioning structure arranged between the obturator and the shot cup.

As noted above, it is considered advantageous for the obturator and also the combined wad component to be moulded from a biodegradable polymer material.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the present invention will now be described with reference to the preferred embodiments shown in the drawings, wherein:

FIG. 1 shows a side view of an obturator according to a preferred embodiment of the present invention;

FIG. 2 shows a transparent view of selected region ‘A’ of the obturator of FIG. 1 ;

FIG. 3 show a top plan view of the obturator of FIG. 1 ;

FIG. 4 shows a shotgun cartridge employing an obturator of the present invention;

FIG. 5 shows a side view of an alternative embodiment of obturator of the present invention;

FIG. 6 shows a perspective view of the obturator shown in FIG. 5 ;

FIG. 7 shows a sectional perspective view of the obturator shown in FIG. 5 ; and

FIG. 8 shows a projectile cartridge wad comprising a further preferred embodiment of the obturator of the present invention;

FIG. 9 shows an alternative projectile cartridge wad in which the cushioning structure is not used; and

FIG. 10 shows a shotgun cartridge employing an alternative obturator according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

The present invention provides for improved obturators for use in projectile cartridges for firearms, such as shotguns. In a projectile cartridge, such as a shotgun cartridge, the main role of the obturator is to provide a gas seal that prevents the dissipation of the gases that are generated during the ignition of the gunpowder within the cartridge. By providing an effective gas seal, the obturator helps to ensure an efficient transfer of the forces generated by the gunpowder to the projectile (e.g. shot) held in the cartridge.

The obturator of the present invention is designed to provide a more reliable gas seal that in turn provides more consistent results when the cartridges are fired.

A preferred embodiment of the obturator 1 of the present invention is shown in FIG. 1 . The obturator 1, which is preferably moulded from a plastic (e.g. polyethylene) or other polymer material and further preferably from a biodegradable polymer material, is formed with a main body 2.

When viewed in plan, the main body 2 has a circular shape that corresponds to the circular shape of the inner walls of a cartridge case or casing (see FIG. 4 ).

Around the periphery of the main body 2 are provided a first annular skirt portion 3 and a second annular skirt portion 4. The first and second annular skirt portions extend away from one another in opposite directions to a free end.

In the preferred embodiment shown in FIG. 1 , both skirts increase in diameter as they extend away from the main body of the obturator towards their respective free ends. In this way the free end of each annular skirt portion is configured to form a seal with the inner wall of a cartridge casing when the cartridge is constructed.

It is envisioned that alternative seal configurations may be employed on the free ends of the annular skirt portions.

For example, in one alternative arrangement each annular skirt may retain a constant diameter as it extends away from the main body of the obturator and instead be provided with a ring that projects outwards from each skirt at the free end thereof. It is this ring that forms a seal with the inner wall of a cartridge casing when the cartridge is constructed.

Also, although the first and second annular skirt portions are shown in FIGS. 1 and 2 as being of equal length, it is envisaged that the respective lengths of the annular skirt portions 3, 4 may differ from one another in some embodiments of the present invention.

In the preferred embodiment shown in FIGS. 1 and 2 , each of the annular skirt portions 3, 4 is provided with a secondary sealing means in the form of a ring 5, 6 that projects outwards from each skirt at a mid-point located somewhere between the free end of the skirt and the point where the skirt joins the main body of the obturator.

As will be appreciated from FIGS. 1 and 2 , the secondary seal rings 5, 6 are shaped so that the extent to which they extend radially out from the skirt increases the closer they get to the free end of their respective annular skirt portion.

It is envisaged that in embodiments of the present invention where an outwardly projecting sealing ring is provided at the free end of each respective skirt, said rings may have a similar shape to the secondary seal rings 5, 6 that are shown in FIGS. 1 and 2 .

The construction of the annular skirt portions 3, 4 will be better appreciated upon consideration of FIG. 2 , which shows a partially exposed close up of region ‘A’ of FIG. 1 .

Also, for increased clarity the annular skirt portions 3, 4 are shown in FIG. 2 as transparent so that the interior of the obturator can be appreciated.

As can be seen from FIG. 2 , in addition to an annular skirt portion, each face of the main body 2 is provided with a centrally located projection 7, 8. In each case the centrally located projection is spaced apart from the annular skirt portion.

That is to say, the first centrally location projection 7 extends from the first face of the main body 2 and is spaced apart from first annular skirt portion 3 and the second centrally location projection 8 extends from the second face of the main body 2 is spaced apart from second annular skirt portion 4.

Spacing each centrally located projection away from their respective annular skirt portion serves to create an annular channel 9 adjacent to each face of the main body. During the firing of a cartridge the annular channel 9 allows pressurised gases to get into the space behind the annular skirt portions and, in so doing, urge the skirts (and their associated seals) outwards towards the inner walls of the cartridge casing and subsequently the gun barrel. In this way an improved gas seal is created between obturator and the walls of the casing/gun barrel.

Turning now to FIG. 3 , which shows the obturator of FIG. 1 in plan, the concentric arrangement of the annular skirt portion 3, annular channel 9 and centrally located projection 7 can be better appreciated.

In the preferred embodiment shown, the centrally located projection 7 is provided with cut out regions that serve to define structural ribs 10, which are shown in an ‘X’ configuration. It is appreciated that alternative cut out arrangements can be adopted without departing from the scope of the present invention. For example, the centrally located projection may be provided with cut outs that achieve castellation or alternatively define one or more co-axially located circular projections.

Although not essential to the operation of the obturator of the present invention, it is considered beneficial to adopt cut out regions in order to reduce the total amount of material used to construct the obturator whilst still maintaining its structural integrity.

Reducing the amount of material required to construct the obturator is particularly advantageous when making it out of biodegradable materials, because otherwise the cost of manufacturing the cartridge might be commercially unattractive.

It is envisioned that the obturator 1 of the present invention can be used in place of a standard powder card in a fibre wad based cartridge. In this regard, FIG. 4 shows a fibre wad cartridge 20 employing the obturator 1 of the present invention.

The cartridge 20 comprises a cartridge casing 21, which is commonly made from plastic and houses the various components of the cartridge. At the base of the cartridge 20 is provided the primer 25, which is usually formed as a brass or nickel head attached to one end of the casing 21.

Adjacent to the primer 25 is the gunpowder charge 24, which is retained within the casing between the primer and the obturator 1. Before the cartridge is fired, the obturator 1 keeps the gunpowder 24 separate from the fibre plug 23.

It is the role of the fibre plug 23 to act as a packer that allows the height of the shot to be adjusted within the cartridge. The fibre plug also provides a cushioning function, which helps to prevent the shot 22 from being deformed by the considerable forces generated by the exploding gunpowder. This is particularly important when the shot (i.e. the cartridge projectile) if formed from softer metals because the shot deformation can greatly affect the firing pattern achieved by a cartridge.

Turning now to FIGS. 5, 6 and 7 , an alternative preferred embodiment of the obturator of the present invention will now be described. The obturator 30 shown in FIG. 5 is similar in construction to that shown in FIG. 1 , with a main body 32 that comprises oppositely extending annular skirt portions 33 and 34.

As before, the annular skirt portions are provided with secondary sealing means in the form of annular rings 35 and 36. Again, the secondary seal rings 35, 36 are shaped so that the extent to which they extend radially outwards increases the closer they get to the free end of their respective annular skirt portion.

Preferably each ring has a generally triangular cross-section. However it is envisioned that alternative configurations (e.g. ‘D’ shaped cross-section) may be adopted provided they still are still capable of achieving a sealing relationship with the inner walls of the cartridge casing/gun barrel.

Although not visible from FIG. 5 , it will be appreciated from FIGS. 6 and 7 that this alternative embodiment of the obturator of the present invention is also provided with the centrally located projections 37, 40 and associated annular channel 38 provided in the obturator shown in FIGS. 1 to 3 .

The main difference between the obturator shown in FIGS. 1 to 3 and the alternative embodiment shown in FIGS. 5 to 7 is the provision of vents 31 a-31 d in the various seals located about the periphery of the obturator 30.

As will be appreciated upon consideration of FIGS. 5 to 7 as a whole, the first annular skirt portion 33 is provided with vent 31 a and the secondary seal on the first annular skirt portion 35 is provided with vent 31 b. Further, the second annular skirt portion 34 is provided with vent 31 d and the secondary seal on the second annular skirt portion 36 is provided with vent 31 c.

Each of the vents 31 a-31 d takes the form of a small cut out channel or groove in the sealing surface of the respective seals. The vents are configured to traverse each seal and allow a limited flow of gases through each of the seals. This limited flow of gas past the obturator's seals is sufficient to prevent the build-up of pressure within a cartridge during manufacture because the speed with which a obturator is inserted into a cartridge casing is much less than the speed of the gases generated when the gunpowder explodes (i.e. during the firing of a gun).

In contrast, the gases generated when the gunpowder in the cartridge is ignited are prevented from leaking past the obturator, which helps to ensure a more efficient transfer of forces from the exploding gunpowder to the cartridge projectiles (e.g. shot) held at the crimped leading end of the cartridge casing.

The effectiveness of the multiple seals' ability to prevent unwanted gas leakage during firing without impairing the cartridge manufacturing process is further enhanced by the off-set arrangement of the vents shown in FIGS. 5 to 7 .

In this regard it will be observed that adjacent vents (e.g. 31 a and 31 b; 31 b and 31 c; etc. . . . ) are located 180 degrees away from one another around the outer perimeter of the obturator 30. By providing the vents off-set in this way the obturator 30 is capable of forming a torturous flow path for any gases that try to by-pass the obturator's gas seals.

Although the obturator shown in FIGS. 5 to 7 has a single vent in each of the obturator's seals, it is envisioned that multiple seals may be provided in each seal. In such an arrangement the vents may or may not be off-set from one another around the periphery of the obturator.

FIGS. 6 and 7 show three dimensional views of the second preferred embodiment of the obturator 30 of the present invention, in which the centrally located projections 37, 40 and the annular channels 38 can be better appreciated.

These figures also clearly show the cut out regions in the centrally located projection 37 that serve to define the structural ribs 39. Although not shown, it should be appreciated that centrally located projection 40 may preferably also provided with a similar arrangement of cut outs regions and structural ribs. Once again it is envisaged that the centrally located projections may have alternative configurations (e.g. castellation or co-axially located circular projections).

Both of the above described embodiments of the obturator of the present invention are shown as having a secondary seal on each annular skirt portion. However it is envisaged that in some embodiments of the present invention a secondary seal may be provided on only one of the annular skirt portions without departing from the present invention.

Conversely, it is also envisioned that if the annular skirt portion is of a suitable length, it may be possible to accommodate more than one secondary seal on that annular skirt portion to further improve the gas sealing function of the skirt.

In a further aspect of the present invention, the obturator of the present invention may be incorporated into a combined wad structure 50. A first preferred embodiment of this combined wad structure 50 is shown in FIG. 8 .

The structure 50, which is preferably moulded as a single unitary construction from a suitable plastics material such as polyethylene, comprises an obturator 51, a cushioning structure 57 and a shot cup 58.

As with the obturators shown in FIGS. 1 to 7 , the obturator 51 of the combined wad structure 50 is provided with a first annular skirt portion 52 and a second annular skirt portion 53. Once again each annular skirt portion 52, 53 is provided with a secondary sealing means in the form of an annular ring (54, 55 respectively). However, as noted above, it is possible that only one of the skirts is provided with a secondary seal or indeed a skirt may be provided with more than one secondary seal.

Also, as with the obturators shown in FIGS. 1 to 7 , the obturator 51 of the combined wad structure 50 is provided with a first centrally located projection that is preferably formed with cut out regions/structural ribs.

However, in order to achieve the unitary construction, the construction of the second centrally located projection is adapted to accommodate the cushioning structure 57, which projects from the opposite face of the obturator to the first centrally located projection.

It will be appreciated that, as with the fibre plug shown in FIG. 4 , the role of the cushioning structure 57 is to minimise the deformation of the shot held within the cartridge when the gunpowder is ignited.

The skilled person will appreciate that the configuration of the cushioning structure can be varied without departing from the general concept of the present invention, that is to say the provision of the improved obturator design.

The cushioning structure 57 serves to connect the obturator 51 to the shot cup 58, within which one or more cartridge projectiles (e.g. shot) are housed in the final cartridge product. Again, the skilled person will be well versed in the structural considerations associated with the shot cup and therefore these will not be covered in any detail here.

It is envisioned that in some variants of the combined wad structure of the present invention, the cushioning structure may be omitted (for example to accommodate a large shot cup). An example this arrangement of combined wad structure 60 is shown in FIG. 9 .

As with the combined wad structure shown in FIG. 8 , the obturator 61 is provided with a first annular skirt portion 62 and a second annular skirt portion 63. In addition, each annular skirt portion 62, 63 is provided with a secondary sealing means in the form of an annular ring (64, 65 respectively). Once again, vents 66 a-66 d may be formed in the obturator 61.

Although not visible in FIG. 9 , it should be appreciated that the obturator 61 is provided with a first centrally located projection that is preferably formed with cut out regions/structural ribs. However, as the shot cup 68 is connected directly to the obturator 61, there are no cut outs in the upper face of the obturator. Instead, the upper face of the obturator effectively forms the base of the shot cup.

It is appreciated that in the arrangement shown in FIG. 9 only the seals formed by the first skirt benefit from being urged outwards (i.e. towards the cartridge casing and the gun barrel) by gases that can get into the cut out regions of the obturator 61. With that said, testing has shown that the seal formed by the second skirt are also urged outwards as they are set back by the extreme forced generated when the gun power of the cartridge is ignited. As a result, effective seals are once again formed and a constant firing outcome is achieved.

FIG. 10 shows a shotgun cartridge 70 employing a variant of the combined wad structure 50 a shown in FIG. 8 . The cartridge has most of the same components as the shotgun cartridge 20 shown in FIG. 4 . As such the same reference numbers are used for those components that are common to both cartridge types.

In this regard, the combined wad structure 50 a is housed within the cartridge casing 21, which is commonly made from plastic and houses the various components of the cartridge. At the base of the cartridge 70 is provided the primer 25, which is usually formed as a brass or nickel head attached to one end of the casing 21.

Adjacent to the primer 25 is the gunpowder charge 24, which is retained within the casing between the primer and the obturator 51 a of the combined wad structure 50 a. The shot 22 is held within the shot cup 58 a of the combined wad structure 50 a. 

1. A projectile cartridge obturator comprising: a main body having a first face with a first centrally located projection spaced apart from a first annular skirt portion located on a periphery of the body and a second face with a second centrally located projection spaced apart from a second annular skirt portion located on the periphery of the body; wherein a free end of each of the first and second annular skirt portions is configured to form a seal with an interior wall of a projectile cartridge case when the obturator is inserted into the case; wherein the first annular skirt portion is further provided with a secondary seal spaced away from the free end of the first skirt portion and wherein said secondary seal also is configured to form a seal with the interior wall of the case.
 2. The obturator of claim 1, wherein the second annular skirt portion is also provided with a secondary seal spaced away from the free end of second skirt portion, wherein said secondary seal also is configured to form a seal with the interior wall of the case.
 3. The obturator of claim 1, further comprising a vent in one or more of the seals formed by the first and second annular skirt portions and the secondary seals.
 4. The obturator of claim 3, wherein the vents are provided in adjacent seals and are offset from one another around the periphery of the body of the obturator.
 5. The obturator of claim 1, wherein the first centrally located projection comprises cut out regions that define one or more structural ribs.
 6. The obturator of claim 5, wherein the second centrally located projection comprises cut out regions that define one or more structural ribs.
 7. The obturator of claim 1, wherein the obturator is formed from a biodegradable material.
 8. A projectile cartridge wad comprising the projectile cartridge obturator of claim
 1. 9. The wad of claim 8, further comprising a fibre plug.
 10. The wad of claim 8, further comprising a cushioning structure and a shot cup.
 11. The wad of claim 10, wherein the cushioning structure is connected to the second centrally located projection of the obturator.
 12. The projectile cartridge wad of claim 11, wherein the obturator, cushioning structure and the shot cup are formed as a single piece.
 13. A projectile cartridge comprising the projectile cartridge obturator of claim 1 or the wad of claim 8 received within a case.
 14. A method of manufacturing a projectile cartridge, said method comprising: moulding an obturator from a polymer material, said obturator comprising a main body having a first face, with a first centrally located projection spaced apart from a first annular skirt portion located on a periphery of the body, and a second face, with a second centrally located projection spaced apart from a second annular skirt portion located on the periphery of the body, wherein at least the first annular skirt portion is provided with a secondary seal spaced away from a free end of the first annular skirt; inserting the obturator into a projectile cartridge case between a charge of gunpowder and one or more cartridge projectiles such that the annular skirts and said secondary seal forms a seal with an interior wall of the cartridge case; and closing the case to encapsulate its contents.
 15. The method of claim 14, wherein the second annular skirt portion is also provided with a secondary seal spaced away from a free end of second skirt portion, said secondary seal also configured to form a seal with the interior wall of the case.
 16. The method of claim 14, further comprising providing each of the annular skirts and said secondary seal with a vent.
 17. The method of claim 16, wherein the vents are provided in adjacent seals and are offset from one another around the periphery of the body.
 18. The method of claim 14, wherein the first centrally located projection, and the second centrally located projection, are moulded with cut outs that define one or more structural ribs.
 19. The method of claim 14, further comprising providing a fibre plug between the obturator and the cartridge projectile.
 20. The method of claim 14, further comprising moulding the obturator as part of a combined wad component that also comprises a cushioning structure and a shot cup, in which the cartridge projectile is received.
 21. The method of claim 14, wherein the obturator is moulded from a biodegradable polymer material. 